The CHF de-peg wasn't really technology risk. Brokers lost money because they undervalued CHF/EUR risk, undervalued liquidity risk (stop orders were executing FAR worse than expected, or simply failing to execute at all), and didn't pay attention to the legal protections afforded to their customers (customer balances went negative but there was no way to recover that money from the customers). These brokers would have had the same problems even if using pen & paper, they failed to plan (or alternatively, made a conscious bet and lost).